1. Field of the Invention
The present invention relates to a controller of an alternator used for vehicle engines, etc.
2. Description of the Related Art
FIG. 4 is a schematic circuit diagram showing a conventional alternator controller.
In FIG. 4, numeral 101 denotes a stator winding; numeral 2 denotes a full-wave rectifier; numerals 201 to 206 denote rectifying diodes; numeral 5 denotes a generating prohibiting circuit; numeral 6 denotes a target charging voltage switching circuit; and numeral 7a denotes an alternator control circuit.
According to a signal of an engine condition signal 10a from an engine control unit 10, a target charging voltage of a battery 3 is switched to any one of a high target charging voltage (VrefH) 603 and a low target charging voltage (VrefL) 605 by a switching element 601. When a voltage of the battery 3 is lower than the target voltage, a comparator 501 outputs xe2x80x9cHxe2x80x9d so as to turn on a transistor 701, which is a switch element, so that a current passes through a field winding 102 which is a rotor winding, thereby generating power in an alternator 1.
In the conventional alternator as above, since a starter motor is used when an engine is started so that a battery voltage is lowered, power generation is started by the alternator just after the engine starting even when any one of the target charging voltages is set, thereby there has been a problem that engine-starting-characteristics deteriorate due to the load of the alternator.
In order to solve the above-mentioned problem, it is an object of the present invention to provide an alternator controller capable of preventing engine-starting characteristics from deterioration due to the load of the alternator in the alternator controller which controls power generation by switching a reference charging voltage for a battery according to a signal from an engine control unit.
In view of the above-mentioned object, an alternator controller according to the present invention comprises: a starting-completion detecting circuit for generating a signal indicating completion of engine starting from a voltage generated by an alternator; a target charging voltage switching circuit for switching a target charging voltage for a battery according to an engine condition signal from an engine control unit; a generation prohibiting circuit for generating a prohibit-power-generation signal when the voltage of the battery is larger than the target charging voltage; a gradual excitation control circuit for generating a gradual excitation control signal according to the engine condition signal from the engine control unit, wherein when an engine starting condition is right at the engine starts, the gradual excitation control circuit gradually initiates generation by the alternator just after the engine starts and when the engine starting condition is wrong, the circuit delays generation by the alternator after the engine starts and then initiates the alternator to generate gradually; and an alternator control circuit for generating an alternator control signal from the starting-completion signal, the prohibit-power-generation signal, and the gradual excitation control signal, wherein the alternator control signal initiates the generation by the alternator according to the gradual excitation control signal when the engine starts and makes the alternator generate according to the prohibit-power-generation signal after the completion of the starting.
The starting-completion detecting circuit may comprise a comparator for detecting the completion of engine starting by comparing the voltage generated by the alternator with a predetermined reference voltage.
Also, the gradual excitation control circuit may comprise a comparator for generating the gradual excitation control signal in which the duty ratio increases gradually based on a comparison between a sawtooth wave and a linear wave increasing with time from the minimum voltage of the sawtooth wave when the engine starting condition is right, and between a sawtooth wave and a linear wave increasing with time from a voltage lower than the minimum voltage of the sawtooth wave when engine starting condition is wrong.
Preferably, the alternator control circuit comprises a switching element connected in series to a field winding of the alternator and a logic circuit for generating a signal by using the starting-completion signal, the prohibit-power-generation signal, and the gradual excitation control signal as inputs, the signal controlling the switching element so as to initiate generation by the alternator according to the predetermined gradual excitation control signal when the engine starts and to make the alternator generate according to the prohibit-power-generation signal after the completion of the starting.